The Reminders window is launched when the company file is opened if any reminders for current or upcoming recurring transactions are scheduled for the current date.
This popup window only appears if you used the Edit Recurring Schedule window to schedule recurring transactions and selected the Reminders option.
The reminders appear in date order. You can choose to record a transaction, skip it for the current period (it will appear again when it's next scheduled), ask to be reminded again the next day, or ask to be reminded again on the due date.